Trim the Windows-only re-exec matrix from four tests to two: one per
launch builder (std = launcher fast path, tokio = `--update` handoff),
each paired with a different captured stream. stdout and stderr flow
through the same handle-inheritance path (GetStdHandle +
SetHandleInformation on the installer side, Stdio::null() on the child),
so the 2x2 product added runtime without adding a distinct invariant.
Also replace the "(issue TBD)" placeholder on open_macos_app_detached
with the issue number.
18a14cec0c